Pm sensor, pm amount sensing device for exhaust gas, and abnormality detection apparatus for internal combustion engine

ABSTRACT

Provided is a PM sensor capable of sensing the amount of particulate matter, and a PM amount sensing device for exhaust gas. Also provided is an abnormality detection apparatus for an internal combustion engine, which is capable of sensing abnormality of a particulate filter. The PM sensor and the PM amount sensing device are mounted in an exhaust pipe of an internal combustion engine. In the exhaust pipe, installed are an air-fuel ratio sensor, a filter, and an air-fuel ratio sensor in sequence in the direction of the flow of exhaust gas. The filter is a compact filter for trapping fine particles. The ECU has a function of calculating a difference ΔI L  between an output I L1  and an output I L2 . Based on ΔI L , it is possible to calculate the amount of particulate matter in the exhaust gas that is currently flowing into the filter.

TECHNICAL FIELD

The present invention relates to a PM sensor, a PM amount sensing devicefor exhaust gas, and an abnormality detection apparatus for an internalcombustion engine.

BACKGROUND ART

Conventionally, as disclosed in, for example, Japanese Patent Laid-OpenNo. 08-284644, there is known an internal combustion engine equippedwith a particulate filter for filtering particulate matter in theexhaust gas. Hereinafter, the particulate matter is also referred tosimply as “particulates”, or “PM”.

The conventional internal combustion engine described above is equippedwith a pressure sensor for detecting a differential pressure of afilter. When exhaust gas containing a large amount of particulates flowsinto a filter, the amount of particulates in the filter increasesaccordingly. The differential pressure of the filter also changesfollowing that as well. Therefore, by sensing the differential pressureof the filter, it is possible to sense the amount of particulates in theexhaust gas.

Besides, as the configuration for sensing the amount of particulates,the configurations of Japanese Patent Laid-Open No. 2007-32490 andJapanese Patent Laid-open No. 2008-64621 are well known.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Laid-Open No. 08-284644-   Patent Literature 2: Japanese Patent Laid-Open No. 2007-32490-   Patent Literature 3: Japanese Patent Laid-open No. 2008-64621

SUMMARY OF INVENTION Technical Problem

As exhaust emission regulations have been tightened in recent years,there is a growing need for sensors for sensing the amount ofparticulates. At the current technological level, however, there is noadvent of on-board type PM sensor or PM amount sensing device, which canwithstand practical use environments. Thus, there are urgent needs fordevelopments of PM sensors and PM amount sensing devices for sensing theamount of particulates. Moreover, when an abnormality occurs in aparticulate filter of an internal combustion engine, an immediatecountermeasure needs to be taken. Thus, technological advancements arealso desired in the abnormality sensing technique for particulatefilters.

The present invention has been made to solve the above describedproblems, and has an object to provide a PM sensor and a PM amountsensing device for exhaust gas, which are capable of sensing the amountof particulate matter.

It is another object of the present invention to provide an abnormalitydetection apparatus for an internal combustion engine, which is capableof detecting abnormality of a particulate filter.

Solution to Problem

To achieve the above-mentioned purpose, a first aspect of the presentinvention is a PM sensor, comprising:

an inlet port through which a portion of gas that is drawn from anexhaust path of an internal combustion engine is allowed to flow in;

a filter for filtering particulate matter (PM) in the gas that hasflowed in through the inlet port;

a heater attached to the filter and capable of changing the temperatureof the filter;

an outlet port through which the gas that has passed through the filteris allowed to flow out to the exhaust path; and

an oxygen concentration sensor element disposed in the outlet port sideand adapted to change its output according to an oxygen concentration ofthe gas that has passed through the filter.

A second aspect of the present invention is the PM sensor according tothe first aspect, further comprising

an oxygen concentration sensor element disposed between the inlet portand the filter and adapted to change its output according to an oxygenconcentration of gas that has flowed in through the inlet port.

A third aspect of the present invention is the PM sensor according tothe second aspect, wherein

the oxygen concentration sensor element of the outlet port side and theoxygen concentration sensor element of the inlet port side are air-fuelratio sensor elements.

A fourth aspect of the present invention is the PM sensor according tothe third aspect, wherein

the air-fuel ratio sensor element includes a heater and upon beingactivated, is heated to a predetermined temperature by the heater, and

the filter and the air-fuel ratio sensor element are spaced apart suchthat the filter comes to a level of temperature at which particulatematter in the filter is not removed when the temperature of the air-fuelratio sensor element is at the predetermined temperature.

To achieve the above-mentioned purpose, a fifth aspect of the presentinvention is a PM amount sensing device for exhaust gas, comprising:

a filter provided in an exhaust path of an internal combustion engineand for filtering particulate matter (PM) in exhaust gas that flowsthrough the exhaust path;

an oxygen concentration sensor element disposed in a downstream of thefilter in the exhaust path, and adapted to change its output accordingto an oxygen concentration of the gas that has passed through thefilter;

a heater attached to the filter;

heating control means for controlling the heater such that the filter isheated until particulate matter in the filter is removed;

temperature reduction control means for controlling the heater such thata temperature of the filter is not higher than a temperature at whichparticulate matter in the filter is not removed, after the control ofthe heating control means;

acquisition means for acquiring an output of the oxygen concentrationsensor element after a temperature of the filter becomes not higher thanthe temperature; and

calculation means for calculating an amount of particulate matter in theexhaust gas based on the output acquired by the acquisition means.

A sixth aspect of the present invention is the PM amount sensing devicefor exhaust gas according to the fifth aspect, wherein

the acquisition means includes means for acquiring an output of theoxygen concentration sensor element when a predetermined time period haselapsed after a temperature of the filter has become not higher than thetemperature, and calculating an integrated value of an amount of exhaustgas that has flowed into the filter before an acquisition timing of theoutput by the acquisition means after a temperature of the filter hasbecome not higher than the temperature, and

the calculation means calculates an amount of particulate matter in theexhaust gas per unit time and per unit volume based on the outputacquired by the acquisition means, the predetermined time, and theintegrated value.

A seventh aspect of the present invention is the PM amount sensingdevice for exhaust gas according to the fifth aspect or the sixthaspect, further comprising

an oxygen concentration sensor element disposed in an upstream of thefilter in the exhaust path, and capable of changing its output accordingto an oxygen concentration of exhaust gas that flows into the filter,wherein

the calculation means calculates an amount of particulate matter in theexhaust gas based on a difference between an output of the oxygenconcentration sensor element of the upstream side of the filter and anoutput of the oxygen concentration sensor element of the downstream sideof the filter.

An eighth aspect of the present invention is the PM amount sensingdevice for exhaust gas according to the seventh aspect, wherein

the oxygen concentration sensor element of the downstream side of thefilter and the oxygen concentration sensor element of the upstream sideof the filter are air-fuel ratio sensor elements.

A ninth aspect of the present invention is the PM amount sensing devicefor exhaust gas according to the eighth aspect, further comprising

calibration means for calibrating an output deviation between theair-fuel ratio sensor of the downstream side of the filter and theair-fuel ratio sensor of the upstream side of the filter.

To achieve the above-mentioned purpose, a tenth aspect of the presentinvention is a PM amount sensing device for exhaust gas, comprising:

a filter provided in an exhaust path of an internal combustion engineand for filtering particulate matter (PM) in exhaust gas that flowsthrough the exhaust path;

a heater attached to the filter;

temperature reduction control means for controlling the heater such thata temperature of the filter is not higher than a temperature at whichparticulate matter in the filter is not removed;

heating control means for controlling the heater such that a temperatureof the filter becomes not lower than a temperature at which particulatematter in the filter is removed, after a predetermined period haselapsed since a temperature of the filter becomes not higher than thetemperature through the control by the temperature reduction controlmeans;

electric energy sensing means for sensing electric energy consumptionconsumed by the heater for removing particulate matter in the filterwhen the control by the heating control means is being performed;

calculation means for calculating an amount of particulate matter of theexhaust gas based on the electric energy consumption sensed by theelectric energy sensing means.

An eleventh aspect of the present invention is the PM amount sensingdevice for exhaust gas according to the tenth aspect, wherein

the electric energy sensing means comprises:

determination means for determining whether or not particulate matter inthe filter is removed after a start of the control by the heatingcontrol means;

electric energy calculation means for calculating electric energyconsumption of the heater during a period from a start of the control bythe heating control means until it is determined that the particulatematter in the filter is removed; and

calculation means for calculating the electric energy consumptionconsumed by the heater for removing particulate matter in the filter,based on the electric energy consumption calculated by the electricenergy calculation means.

A twelfth aspect of the present invention is the PM amount sensingdevice for exhaust gas according to the eleventh aspect, comprising:

an upstream side oxygen concentration sensor disposed in an upstream ofthe filter in the exhaust path, and adapted to change its outputaccording to an oxygen concentration of gas that flows into the filter;and

a downstream side oxygen concentration sensor disposed in a downstreamof the filter in the exhaust path, and adapted to change its outputaccording to an oxygen concentration of gas that flows out from thefilter, wherein

the determination means determines whether or not the particulate matterin the filter is removed based on a difference between an output of theupstream side oxygen concentration sensor and an output of thedownstream side oxygen concentration sensor.

To achieve the above-mentioned purpose, a thirteenth aspect of thepresent invention is an abnormality detection apparatus for an internalcombustion engine, comprising:

an oxygen concentration sensor disposed in a downstream of a particulatefilter provided in an exhaust path of the internal combustion engine,and adapted to change its output according to an oxygen concentration ofgas that flows out from the particulate filter;

heating means for heating the particulate filter so as to regenerate theparticulate filter; and

detection means for detecting an abnormality of the particulate filterbased on an output of the oxygen concentration sensor of the downstreamafter the regeneration of the particulate filter.

The abnormality detection apparatus for an internal combustion engineaccording to the thirteenth aspect, further comprising

an oxygen concentration sensor disposed in an upstream of theparticulate filter and adapted to change its output according to anoxygen concentration in exhaust gas, wherein

the detection means detects an abnormality of the particulate filterbased on a difference between an output of the oxygen concentrationsensor of the upstream and an output of the oxygen concentration sensorof the downstream.

The abnormality detection apparatus for an internal combustion engineaccording to the fourteenth aspect, wherein

the oxygen concentration sensor disposed in each of the upstream and thedownstream of the particulate filter respectively is an air-fuel ratiosensor.

Advantageous Effects of Invention

According to a first aspect of the present invention, an oxygenconcentration sensor element exhibits an output with lower oxygenconcentration as the amount of particulates in a filter increases. Basedon the output of the oxygen concentration sensor element, it is possibleto detect the amount of particulates in the gas that flows into thefilter. Further, since the particulates in the filter can be removed byheating with a heater, it is possible to repeatedly perform the sensingof the amount of particulates.

According to a second aspect of the present invention, an oxygenconcentration sensor element is provided in each of the upstream side offilter and the downstream side of filter. The difference between theoutputs of these oxygen concentration sensor elements correspond withhigh precision to the amount of particulates in the filter. Thus, basedon the difference between the outputs of these oxygen concentrationsensor elements, it is possible to sense with high precision the amountof particulates in the gas that flows into the filter.

According to a third aspect of the present invention, an air-fuel ratiosensor element is used as the oxygen concentration sensor element in thefirst and second aspects of the present invention. The air-fuel ratiosensor has a proven track record as the sensor for sensing the oxygenconcentration of exhaust gas. By using an air-fuel ratio sensor element,it is possible to sense the amount of particulates in the exhaust gaswith high reliability.

According to a fourth aspect of the present invention, the followingeffects can be obtained. The air-fuel ratio sensor generally operateswhile being heated to a predetermined activation temperature. On theother hand, when the temperature of the filter rises to not lower than aspecific temperature, particulates will burn off without beingaccumulated in the filter. According to the fourth aspect of the presentinvention, it is ensured that the filter can hold particulates evenwhile the temperature of the air-fuel ratio sensor is at the activationtemperature. As a result, it is possible to sense the amount ofparticulates in the exhaust gas even while the air-fuel ratio sensor isat the activation temperature.

According to a fifth aspect of the present invention, after the filteris heated to a sufficiently high temperature, a heater is controlledsuch that the temperature of the filter is lowered to a level at whichparticulates can be trapped. After the heater control, particulates goon being trapped in the filter, and the output of the oxygenconcentration sensor element is acquired. The greater the amount ofparticulates in the filter, the lower the oxygen concentration in thegas in the downstream of filter becomes, and the output of the oxygenconcentration sensor element exhibits a lower oxygen concentrationvalue. Therefore, based on the output of the oxygen concentration sensorelement, it is possible to calculate the amount of particulates in thegas that flows into the filter. This allows the sensing of the amount ofparticulates in the exhaust gas.

According to a sixth aspect of the present invention, it is possible tocalculate the amount of particulates in the exhaust gas per unit timeand per unit volume.

According to a seventh aspect of the present invention, an oxygenconcentration sensor element is provided in each of the upstream side offilter and the downstream side of filter. The difference between theoutputs of these oxygen concentration sensor elements corresponds withhigh precision to the amount of particulates in the filter. Thus, basedon the difference between the outputs of these oxygen concentrationsensor elements, it is possible to sense with high precision the amountof particulates in the gas that flows into the filter.

According to an eighth aspect of the present invention, an air-fuelratio sensor element is used as the oxygen concentration sensor element.The air-fuel ratio sensor has a proven track record as the sensor forsensing the oxygen concentration of exhaust gas. Thus, by using anair-fuel ratio sensor element, it is possible to sense the amount ofparticulates in the exhaust gas with high reliability.

According to a ninth aspect of the present invention, the outputdiscrepancy among a plurality of air-fuel ratio sensors can becalibrated. This makes it possible to perform the sensing of the amountof particulates with a higher precision.

According to a tenth aspect of the present invention, it is possible tosense the amount of particulates. The greater the amount of particulatesin the exhaust gas, the greater the amount of particulates to be trappedin the filter per unit time becomes. The greater the amount ofparticulates in the filter, the greater the electric energy consumptionof heater needed to remove the particulates in the filter becomes.Therefore, it is possible to calculate the amount of particulates in thegas that flows into the filter based on the electric energy consumptionof heater.

According to an eleventh aspect of the present invention, it is possibleto accurately calculate the electric energy consumption that has beenconsumed at the heater until the particulates in the filter has beenremoved.

According to a twelfth aspect of the present invention, it is possibleto determine with high precision whether or not the particulates in thefilter are removed.

According to a thirteenth aspect of the present invention, an oxygenconcentration sensor is provided in the downstream of a particulatefilter. If the particulate filter is in a condition to be able tonormally trap particulates, the particulates will go on accumulating inthe filter so that the effect of the accumulation of particulates shouldmanifest itself in the output of the oxygen concentration sensor.Therefore, based on the output of the oxygen concentration sensor, it ispossible to detect abnormality of the particulate filter.

According to a fourteenth aspect of the present invention, an oxygenconcentration sensor element is provided in each of the upstream anddownstream of a particulate filter. The difference between the outputsof these oxygen concentration sensor elements corresponds with highprecision to the amount of particulates in the particulate filter. Basedon the difference between the outputs of these oxygen concentrationsensor elements, it is possible to detect abnormality of the particulatefilter with high reliability.

According to a fifteenth aspect of the present invention, an air-fuelratio sensor is used as the oxygen concentration sensor in thefourteenth aspect of the present invention. The air-fuel ratio sensorhas a proven track record as the sensor for sensing the oxygenconcentration of exhaust gas. By using the air-fuel ratio sensor, it ispossible to detect the abnormality of particulate filter with highreliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram to show the configuration of a PM sensor and PMamount sensing device for exhaust gas according to Embodiment 1 of thepresent invention.

FIG. 2 is a diagram to show the view of the configuration of FIG. 1 seenfrom the direction of arrow A.

FIG. 3 is a time chart to illustrate the operation of sensing the amountof PM relating to Embodiment 1.

FIG. 4 is a flowchart of a routine performed by ECU 50 in Embodiment 1.

FIG. 5 is a diagram to show an example of the map of the correlationline between the value of ΔI_(L) and the amount of particulates (theamount of PM).

FIG. 6 is a flowchart of a routine performed by ECU 50 in Embodiment 2according to the present invention.

FIG. 7 is a diagram to show the configuration of an abnormalitydetection apparatus of an internal combustion engine relating toEmbodiment 3 of the present invention.

FIG. 8 is a flowchart of a routine performed by ECU 50 in Embodiment 3according to the present invention.

REFERENCE SIGNS LIST

-   2 an internal combustion engine-   10 an exhaust pipe-   20 a partition-   22, 24 an air-fuel ratio sensor (A/F sensor)-   30 a filter-   34 a heater control part-   50 ECU (Electronic Control Unit)-   130 DPF

DESCRIPTION OF EMBODIMENTS Embodiment 1 Configuration of Embodiment 1

FIG. 1 is a diagram to show the configuration of a PM sensor and PMamount sensing device for exhaust gas according to Embodiment 1 of thepresent invention. FIG. 2 is a diagram to show the view of theconfiguration of FIG. 1 seen from the direction of arrow A. The PMsensor and the PM amount sensing device for exhaust gas according toEmbodiment 1 are suitable for internal combustion engines of vehicles.

The PM sensor and the PM amount sensing device according to Embodiment 1are mounted on an exhaust pipe 10 of an internal combustion engine 2.There is no limitation on the number and type of cylinders of theinternal combustion engine 2. It is noted that the internal combustionengine 2 of FIG. 1 is schematically shown for the sake of convenience.In the exhaust pipe 10, installed are an air-fuel ratio sensor 22, afilter 30, and an air-fuel ratio sensor 24 in sequence in the directionof the flow of exhaust gas. In the following description below, for thesake of simplicity, the air-fuel ratio sensor is also referred to as“A/F sensor.” In Embodiment 1, a partition 20 shown in FIG. 1 isprovided. The partition 20 opens into the left side on the page and theright side on the page of FIG. 1. Exhaust gas flows from the left sideon the page of FIG. 1 to the right side on the page of FIG. 1 throughthe inside of the partition 20.

The filter 30 is a compact filter for trapping fine particles. Thefilter 30 is a small-sized version of the so-called diesel particulatefilter (DPF). Hereinafter, particulate matter (PM) is also referred tosimply as “particulates” or “PM”.

A part of the exhaust gas flowing in the exhaust pipe 10 of the internalcombustion engine 2 flows into the filter 30. The filter 30 can filterparticulates in the exhaust gas that flows thereinto. According to this,the particulates go on accumulating within the filter 30. As a result,the filter 30 can capture and collect (that is, trap) particulates.

The filter 30 can be formed by imitating the material and specificconfiguration of a DPF, and making its outer shape smaller than that ofthe DPF. The detailed structure of the filter 30 needs not necessarilybe the same as or analogous to the DPF. As shown in FIG. 2, theouter-shape dimension of the filter 30 is smaller compared to the innerdiameter of the exhaust pipe 10. Therefore, a portion of the exhaust gasflows into the filter 30, and the remaining gas goes on flowing to thedownstream of the exhaust pipe 10 without flowing into the filter 30.

A/F sensors 22 and 24 are A/F sensors of limiting current type. The A/Fsensor of limiting current type exhibits a different limiting currentvalue according to the oxygen concentration of the atmosphere, in otherwords, the oxygen concentration of the gas to be detected. The limitingcurrent value proportionally varies according to the oxygenconcentration. Therefore, the A/F sensor 22 changes its output accordingto the oxygen concentration of the exhaust gas in the upstream of thefilter 30. Moreover, the A/F sensor 24 changes its output according tothe oxygen concentration of the exhaust gas in the downstream of thefilter 30 as well.

The A/F sensors 22 and 24 each includes an outer electrode that isexposed to the gas to be detected, that is, the exhaust gas, an innerelectrode which is exposed to the atmosphere, and an oxygen-ionconducting electrolyte interposed between the outer electrode and theinner electrode. The oxygen-ion conducting electrolyte favorablyutilizes, for example, ZrO₂ which has a high reliability. Since there isnot particular limitation on the specific configurations of the A/Fsensors 22 and 24, further description thereof will be omitted.

The A/F sensors 22 and 24 are heated to a predetermined activationtemperature by a built-in heater, and thereafter perform the sensing ofair-fuel ratio at the activation temperature. As shown in FIG. 1, thefilter 30 and the A/F sensor 22 or 24 are spaced apart by apredetermined distance. The distance between the filter 30 and the A/Fsensor 22 or 24 is large enough such that particulates can be presentwithout being burnt within the filter 30 even when the A/F sensors 22and 24 are at the activation temperature.

The filter 30 includes a heater 32 which is a compact heater. The heater32 connects to a heater control part 34. The heater 32 can keep theinside of the filter 30 at a high temperature so that particulateswithin the filter 30 can be removed. This makes it possible to reducethe amount of particulates in the filter 30 to be zero, therebyperforming the regeneration of the filter 30 (regeneration of trappingcapability).

In Embodiment 1, an ECU (Electronic Control Unit) 50 connects to the A/Fsensors 22 and 24, and the heater control part 34. The ECU 50 canacquire the outputs of the A/F sensors 22 and 24, respectively.Hereinafter, for the sake of convenience, the limiting current value ofthe A/F sensor 22 is also referred to as an output current value I_(L1),or an output I_(L1); and the limiting current value of the A/F sensor 24is referred to as an output current value I_(L2), or an output I_(L2).Moreover, in Embodiment 1, the ECU 50 prestores the arithmeticprocessing to calculate the difference between the output I_(L1) and theoutput I_(L2). Hereinafter, the difference between the output I_(L1) andthe output I_(L2) is also referred to as ΔI_(L).

Moreover, the ECU 50 can provide the heater control part 34 with acontrol signal to perform on-off control of the heater 32 and regulationof its heat generation rate.

It is noted that in Embodiment 1, although not illustrated, the ECU 50also connects to a sensor (for example, an intake pressure sensor or anair flow meter) for measuring the amount of intake air of the internalcombustion engine 2, which is located in the upstream of the exhaustpipe 10. The ECU 50 can measure an intake air amount Ga of the internalcombustion engine 2 based on the output of the above described sensor.In Embodiment 1, the ECU 50 stores the routine to calculate an exhaustgas amount Gexh based on the intake air amount Ga.

[Operation of Embodiment 1] (PM Detection Principle Relating toEmbodiment 1)

Having continued diligent research, the present inventors came up withthe idea of a method for sensing the amount of particulates based anovel detection principle which has been unknown. That is, whenparticulates are filtered by a compact filter like the filter 30, thediffusion distance of the gas (oxygen: O₂) that passes through insidethe compact filter varies.

The greater the amount of particulates in the filter, the longer thediffusion distance of the gas that passes through the compact filterbecomes. The amount of O₂ that can pass through the compact filterdecreases as the amount of particulates in the filter increases; and asa result of that, the oxygen concentration in the downstream of thecompact filter goes on declining. Therefore, it is possible to sense theamount of particulates in the gas that flows into the compact filterbased on the oxygen concentration in the downstream of the compactfilter.

In the above described series of phenomena, the compact filter plays thesame role as that of a diffusion-controlled layer in a limiting currenttype A/F sensor. When the limiting current type A/F sensor is disposedin the downstream of the compact filter, the diffusion distance ofoxygen in a layer which is the total of the compact filter and thediffusion-controlled layer of the limiting current type A/F sensor,increases as the amount of particulates in the filter increases. As aresult of that, as the amount of particulates within the filterincreases, the limiting current value of the limiting current type A/Fsensor in the downstream goes on declining.

When a limiting current type A/F sensor is disposed respectively in theupstream and the downstream of the compact filter, as the amount ofparticulates in the filter increases, the difference between the outputsof the limiting current type A/F sensors of the upstream and thedownstream increases. Therefore, it is possible to sense the amount ofparticulates in the gas that flows into the compact filter based on thedifference between the outputs of the limiting current type A/F sensorsof the upstream and the downstream.

(Specific Operation of Embodiment 1)

When exhaust gas having a certain air-fuel ratio and a certain amount ofparticulates flows into the filter 30, the A/F sensor 22 exhibits aspecific output corresponding to the air-fuel ratio. On the other hand,the output of the A/F sensor 24 varies according to the amount ofparticulates in the filter 30 as described above. As a result of theexhaust gas continually flowing into the filter 30, the amount ofparticulates in the filter 30 increases. As the amount of particulatesin the filter 30 increases, the oxygen concentration of the atmosphereof the A/F sensor 24 declines, and thereby I_(L2) declines. As a resultof this, since the output I_(L2) goes on declining while the outputI_(L1) stays constant, ΔI_(L) increases.

Under the condition of the same time period and the same flow rate ofexhaust gas, the greater the amount of particulates contained in theexhaust gas, the further ΔI_(L) increases. Therefore, based on ΔI_(L),it is possible to calculate the amount of particulates of the exhaustgas that currently flows into the filter 30. According to this, theamount of particulates generated in the internal combustion engine 2 canbe sensed.

The method for sensing the amount of PM of Embodiment 1 will bedescribed more specifically using FIG. 3. FIG. 3 is a time chart toillustrate the operation of sensing the amount of PM relating toEmbodiment 1. In the operation of sensing the amount of PM of Embodiment1, three steps of A, B, and C are repeatedly performed. In Embodiment 1,it is supposed that the A/F sensors 22 and 24 are kept constant at theactivation temperature.

In step A, first, a control signal is sent to the heater control part 34from the ECU 50 so that the heating of the heater 32 is performed. Theheating of the heater 32 will result in that the particulates in thefilter 30 is removed (burnt) and the particulates in the filtertemporarily becomes zero. Moreover, in Embodiment 1, in order toeliminate the discrepancy of output (output deviation) between the A/Fsensor 22 and the A/F sensor 24, a zero-point correction of output isalso performed in step A. This zero-point correction of output allowsthat ΔI_(L) indicates with high precision a value corresponding to theamount of particulates in the filter 30.

In step B, the heater 32 is turned off. This will cause the temperatureof the filter 30 to be lowered so that particulates start to beaccumulated in the filter 30. In step B, such a state is maintainedturning into a standby state until a predetermined time period haselapsed.

In step C, upon elapse of the predetermined time period from step B, theECU 50 acquires the output I_(L1) and the output I_(L2) to calculateΔI_(L). Based on the above described predetermined time period from stepB to step C (that is, the period for trapping particulates) and thetotal of the exhaust gas amount Gexh that has passed during the timeperiod, the amount of particulates per unit time and unit gas amount iscalculated.

After step C, step A is performed in succession. Thereafter, byrepeatedly performing steps A, B, and C, it is possible to continuouslysense the amount of particulates. According to Embodiment 1, it ispossible to continuously perform a quantitative sensing of particulatesof exhaust gas for every predetermined time period (predetermined cycle)during the operation of the internal combustion engine 2.

As described so far, according to Embodiment 1, it is possible to sensethe amount of particulates of the exhaust gas that flows into the filter30 based on the change amount of the output (the decline amount of theoutput) of A/F sensor 24, that is ΔI_(L). Moreover, according toEmbodiment 1, an A/F sensor may be provided in each of the upstream sideof the filter 30 and the downstream side of the filter 30. By measuringthe difference ΔI_(L) between the A/F sensors 22 and 24, it is possibleto sense with high precision the increase in the amount of particulatesin the filter 30. As a result of that, it is possible to sense with highprecision the amount of particulates in the gas that flows into thefilter.

Moreover, according to Embodiment 1, since the particulates of thefilter 30 can be heated and thereby removed by the heater 32, it ispossible to repeat the sensing of the amount of particulates. The filter30 is compact, and the electric energy consumption of the heater 32 willbe small even if the heating for removing particles is repeated. Thus,the effect on the fuel economy can be suppressed to be low.

Moreover, according to Embodiment 1, it is possible to sense the amountof particulates of exhaust gas by utilizing the A/F sensors 22 and 24.The air-fuel ratio sensor has a proven track record as the sensor forsensing the oxygen concentration of exhaust gas. By using an air-fuelratio sensor, it is possible to sense the amount of particulates in theexhaust gas with a high reliability.

Moreover, an air-fuel ratio sensor generally operates while being heatedto a predetermined activation temperature. If the temperature of thefilter 30 rises to not lower than a specific temperature (a burningtemperature of particulates), particulates will burn off without beingaccumulated in the filter 30. In this connection, according toEmbodiment 1, the A/F sensors 22 and 24 and the filter 30 are spacedapart. Therefore, it is ensured that the filter 30 can hold particulateseven while the temperature of the A/F sensors 22 and 24 are at theactivation temperature. As a result, it is possible to sense the amountof particulates in the exhaust gas even while the A/F sensors 22 and 24are at the activation temperature. Further, according to Embodiment 1,the temperature of the A/F sensors 22 and 24 is kept constant at theactivation temperature, and the temperature dependency of the output ofthe A/F sensors 22 and 24 is small. Therefore, Embodiment 1 does notneed the temperature correction of output and a temperature sensor fortemperature correction, and therefore is advantageous.

[Specific Processing of Embodiment 1]

Hereinafter, specific processing performed by the PM amount sensingdevice for exhaust gas according to Embodiment 1 will be described byusing FIG. 4. FIG. 4 is a flowchart of a routine performed by ECU 50 inEmbodiment 1. The routine of FIG. 4 are executed during the startup ofthe internal combustion engine 2. FIG. 5 is a diagram to show an exampleof the map of the correlation line between the value of ΔI_(L) and theamount of particulates (the amount of PM). Correlation linesrespectively for air-fuel ratios 20 and 25 are shown in FIG. 5. InEmbodiment 1, the correlation map for air-fuel ratio=20 shown in FIG. 5is prestored in the ECU 50.

In the routine shown in FIG. 4, first, A/F sensor heating and heatercontrol are performed (step S100). In this step, after the startup ofthe internal combustion engine 2, the heater incorporated in each of theA/F sensors 22 and 24 is controlled for heating until the A/F sensors 22and 24 become activated. At the same time, the heater 32 is alsocontrolled so that the filter 30 is heated to a burning temperature ofparticulate.

Next, after the determination of sensor activation and PM burning, azero-point correction of output for the A/F sensors is performed (stepS102). In this step S102, first, it is determined whether or not the A/Fsensors 22 and 24 are activated. The determination of sensor activationcan be performed by, for example, whether or not the error of the outputof the A/F sensor 22 or 24 is within a predetermined range. Moreover, inthis step S102, the determination of PM burning is also performed. Thedetermination of PM burning is performed to determine whether or notparticulates adhered to the filter 30 have burnt off completely. InEmbodiment 1, it is determined that particulates have completely burntoff if the heating of the filter 30 by the heater 32 is continued for apredetermined time period.

In step S102, a zero-point correction of output for the A/F sensors isperformed as well. The zero-point correction of output for the A/Fsensor is performed to eliminate the discrepancy of output (outputdeviation) between the A/F sensor 22 and the A/F sensor 24. Thiszero-point correction of output, for example, can be performed asfollows. First, a power factor k to be multiplied against the outputcurrent of the A/F sensor 24 is derived such that the output of the A/Fsensor 22 agrees with the output of the A/F sensor 24. This factor k ismultiplied against the output current of the A/F sensor 24. This allowsthe difference between outputs to be cancelled every time the processingof step S102 is performed thus realizing a zero-point correction ofoutput.

Next, the heater 32 is turned off (step S104). When the heater 32 isturned off, the temperature of the filter 30 is lowered and, after awhile, the filter 30 is sufficiently cooled to a temperature at whichparticulates can be accumulated within the filter 30. Thereafter,particulates go on accumulating in the filter 30.

After the heater is turned off, the determination processing of filtertemperature is executed for ECU 50 to determine whether or not thetemperature of the filter 30 is lowered to a level where particulatescan be accumulated. In this filter temperature determination, forexample, the determination on whether or not the temperature of theheater 32 is sufficiently lowered may be made based on the comparisonbetween the resistance value of the heater 32 and a predetermined value.It may be determined that the temperature of the filter 30 issufficiently low when the heater 32 is at a sufficiently lowtemperature. Alternatively, it may be determined that the temperature ofthe filter 30 is sufficiently lowered when ΔI_(L) increases to apredetermined criterion. When a fulfillment of the condition of thedetermination processing of

24 and the storing of the exhaust gas amount may be performed afterelapse of the predetermined time period T₀. When the engine operatingregion in which sensing of the amount of PM is desired to be performedis determined, or when sensing of the amount of PM is desired to beperformed while the amount of generated particulates is considerablylarge in the view point of sensing accuracy, the operating conditionswhen the sensing of the amount of PM is performed may be defined inadvance.

After step S108, the processing of ΔI_(L) calculation is performed (stepS110). In this step, first, difference between the output values thatare stored in step S108 is calculated. Next, in Embodiment 1, thedifference obtained by that calculation is converted into a referencecurrent value according to the air-fuel ratio and the exhaust gas amountGexh. In Embodiment 1, the reference current value is supposed to be theoutput current value of the A/F sensor 22 or 24 when the air-fuelratio=20, and exhaust gas amount=10 g/s. The reference is unified bythis conversion and a final ΔI_(L) is calculated.

Next, the processing to calculate the amount of PM from a correlationline is performed (step S112). In step S112, a map in which thecorrelation line for air-fuel ratio=20 is defined as shown in FIG. 5 isreferred to calculate the amount of PM according to ΔI_(L) afterconversion. Specifically, in this processing, as ΔI_(L) increases, thecalculated amount of PM increases as shown in the map of FIG. 5.

The following effects are achieved by the above described steps S110 andS112. For example, as shown in FIG. 5, the difference ΔI_(L2) that isobtained when air-fuel ratio=25-coincides with the difference ΔI_(L2)when air-fuel ratio=20, by being converted into a reference currentvalue. The relationship between the amount of PM and ΔI_(L) variesaccording to the air-fuel ratio of exhaust gas. As shown in FIG. 5, whenΔI_(L1) is obtained when air-fuel ratio is 20, the amount of PMcorresponding to this ΔI_(L1) is determined. On the other hand, ifΔI_(L2) is obtained when air-fuel ratio is 25, it will be the samevalue, as the amount of PM, as ΔI_(L2) when air-fuel ratio=20, even ifΔI_(L2) is larger than ΔI_(L2). In Embodiment 1, the difference betweenthe outputs of the A/F sensors 22 and 24 that are obtained at differentair-fuel ratios of exhaust gas is converted into a value according toair-fuel ratio=20 through the conversion processing of step S110.Besides this conversion being performed, a map is referred to in whichthe correlation line for air-fuel ratio=20 is defined. This makes itpossible to accurately sense the amount of PM based on the outputs ofthe A/F sensors 22 and 24 even under the situation where the air-fuelratio varies every moment.

Next, the amount of PM according to the amount of exhaust gas iscalculated (step S114). In this step, the amount of particulates perunit time and per unit gas amount are calculated based on the integratedexhaust gas amount Gexh_itg stored in step S108 and a predetermined timeperiod T_(o). This makes it possible to perform quantitative evaluationof particulates in the exhaust gas.

Next, the heater 32 is heated again and particulates in the filter 30are removed (step S116). Thereafter, the process returns to step S102,and the processing after step S102 are repeatedly executed.

According to the above described processing, it is possible to sense theamount of particulates in the exhaust gas.

It is noted that the map in which the relation between ΔI_(L) and theamount of PM to be stored in the ECU 50 may be a so-calledmulti-dimensional map in which correlation lines are defined formultiple air-fuel ratios including 20, 25 and others. By utilizing this,the amount of PM may be calculated by directly referring to thecorrelation lines for each air-fuel ratio without performing theconversion into the reference current value of step S110. Moreover, inEmbodiment 1, the ECU 50 calculates the exhaust gas amount Gexh based onthe intake air amount Ga. Therefore, it is possible to use an integratedvalue of the intake air amount Ga in place of the integrated exhaust gasamount Gexh_itg.

It is noted that in Embodiment 1 described above, the filter 30corresponds to the “filter” in the first invention, the heater 32corresponds to the “heater” in the first invention, and the A/F sensor24 corresponds to the “oxygen concentration sensor element” in the firstinvention, respectively. Moreover, in Embodiment 1, the A/F sensor 22corresponds to the “oxygen concentration sensor element” in the secondinvention.

It is noted that in Embodiment 1 described above, the filter 30corresponds to the “filter” in the fifth invention; the air-fuel ratiosensor 24 to the “oxygen concentration sensor element” in the fifthinvention; and the heater 32 to the “heater” in the fifth invention,respectively. Moreover, in Embodiment 1, the “heating control means” inthe fifth invention is implemented by the ECU 50 executing theprocessing of step S100 or step S116; the “temperature reduction controlmeans” in the fifth invention by the ECU 50 executing the processing ofstep S104; the “acquisition means” of the fifth invention by the ECU 50executing the processing of step S108; and the “calculation means” ofthe fifth invention by the ECU 50 executing the processing of steps S110to S114, respectively in the routine of FIG. 4.

Moreover, in Embodiment 1, the predetermined time period T₀ correspondsto the “predetermined time period” in the sixth invention, and theintegrated exhaust gas amount Gexh_itg to the “integrated value” in thesixth invention, respectively.

Furthermore, in Embodiment 1, the “calibration means” in the ninthinvention is implemented by the ECU 50 executing the processing of stepS102 in the routine of FIG. 4.

[Variant of Embodiment 1] [First Variant]

In Embodiment 1, the A/F sensors 22 and 24 utilize an air-fuel ratiosensor of limiting current type. The present invention, however, is notlimited to this. As described above, as the amount of particulates inthe filter 30 increases, the amount of O₂ that can pass through acompact filter decreases, and consequently the oxygen concentration inthe downstream of the filter 30 goes on declining. Embodiment 1 utilizesthis phenomenon to sense the amount of particulates in the gas thatflows into the filter 30 based on the oxygen concentration in thedownstream of the filter 30. In this connection, any air-fuel ratiosensor of type other than the limiting current type, for example, anair-fuel ratio sensor of two-cell type may be used in place of the A/Fsensors 22 and 24. Moreover, any oxygen concentration sensor other thanthe air-fuel ratio sensor, which can linearly measure the oxygenconcentration of gas, may be used in place of the A/F sensors 22 and 24.

(Second Variant)

In Embodiment 1, one A/F sensor is provided for each of the upstream andthe downstream of the filter 30. The present invention, however, is notlimited to this. As described above, as the amount of particulates inthe filter 30 increases, the amount of O₂ that can pass through acompact filter decreases, and consequently the oxygen concentration inthe downstream of the filter 30 goes on declining. Therefore, an A/Fsensor may be provided only in the downstream of the filter 30 so thatthe decline amount of the output (hereafter, ΔI_(Ld)) of this A/F sensormay be used in place of ΔI_(L). However, when an A/F sensor or an oxygenconcentration sensor is provided only in the downstream of the filter,it is not possible to sense the oxygen concentration of exhaust gas inthe upstream of the filter 30. In this case, for example, the differencebetween the air-fuel ratio or the oxygen concentration, which iscalculated based on the operating condition of the internal combustionengine 2, and the output of the A/F sensor or the oxygen concentrationsensor in the downstream of the filter may be utilized as ΔI_(L).

(Third Variant)

In Embodiment 1, the “PM sensor” relating to the first invention isconfigured by combining the A/F sensors 22 and 24, the filter 30, andthe heater 32, respectively as discrete parts. The present invention is,however, not limited to this configuration. A single PM sensor may befabricated in which the functions of the element parts of the A/Fsensors 22 and 24, the filter 30 and the heater 32 are integrated(unified).

Specifically, a filter for filtering PM is provided in a case for the PMsensor which includes an inlet port of exhaust gas and an outlet port ofexhaust gas. Further, an air-fuel ratio sensor element part or an oxygenconcentration sensor element part is provided respectively in theupstream and the downstream of the filter. A heater for heating thefilter is also incorporated. As described so far, there is provided a PMsensor which includes an inlet port and an outlet port of exhaust gas,and incorporates a filter, an oxygen concentration sensor element part,and a heater. When this PM sensor is disposed in the exhaust path, partof the exhaust gas is drawn out via the outlet port to flow into theinside of the case for PM sensor. The exhaust gas that has flowed fromthe inlet port passes through the filter, and thereafter flows out fromthe outlet port into the exhaust path again. In this configuration, itis possible to sense the amount of particulates in the exhaust gas bytreating the difference in the outputs of the oxygen concentrationsensors of the upstream and downstream of the filter, in the same manneras ΔI_(L) of Embodiment 1.

According to the unified PM sensor relating to the present variant,since the effects of the flow rate of exhaust gas and the air-fuel ratioare reduced compared with the configuration of Embodiment 1, it ispossible to perform the sensing of the amount of PM with high precisionwithout being subject to these effects. When performing the abovedescribed unification, it is preferable that thermal insulation aroundthe filter is sufficiently ensured so that the filter can holdparticulates even while the temperature of the air-fuel ratio sensorelement is at the activation temperature. It is noted that as describedin the second variant above, an air-fuel ratio sensor element part or anoxygen concentration sensor element part may be provided only in thedownstream of the filter.

(Fourth Variant)

It is noted that in Embodiment 1, the following variation of thecalculation process is possible as well. First, the ECU 50 stores a map(first map) between the value of I_(L1) and the value of I_(L2), and theoxygen concentration. Moreover, the ECU 50 is also made to store a map(second map) of correlation lines that define the relationship betweenthe oxygen concentration difference ΔO₂ between the upstream and thedownstream of the filter 30, and the amount of PM. This second map canbe defined such that the larger the oxygen concentration difference ΔO₂,the larger the amount of PM becomes. After the ECU 50 acquires I_(L1)and I_(L2) in step S108, an oxygen concentration value corresponding tothose values is calculated according to the above described first map.Next, based on the difference of the oxygen concentration values, theamount of PM is calculated according to the second map. Such calculationprocess may substitute for the processing of steps S110 and S112.

Embodiment 2 Configuration of Embodiment 2

The PM amount sensing device of Embodiment 2 has a configuration inwhich a circuit for measuring the electric power consumption of theheater 32 is added to the configuration of Embodiment 1. There is nolimitation on the specific configuration of this circuit, and anycircuit having a current sensor and a voltage sensor for measuring thecurrent and applied voltage of the heater 32 may be used. Since,excepting this point, the hardware configurations of Embodiment 1 andEmbodiment 2 are the same, the hardware configuration of Embodiment 2will not be illustrated for simplifying the description. The PM amountsensing device of Embodiment 2 may be implemented by causing the ECU 50to execute the routine shown in FIG. 6 in the above describedconfiguration.

In the following description, the electric power consumption of theheater 32 will also be referred to as “P_(H)”. Moreover, a quantityobtained by a time integration of the electric power consumption P_(H)of the heater 32, that is, the electric energy consumption of the heater32, is also referred to as “W_(H)”.

[Operation of Embodiment 2]

The greater the amount of particulates in the exhaust gas, the greaterthe amount of particulates to be trapped in the filter 30 per unit timebecomes. The greater the amount of particulates in the filter 30, thegreater the electric energy consumption of the heater 32 needed toremove the particulates in the filter 30 becomes. Accordingly, inEmbodiment 2, the amount of particulates in the gas that flows into thefilter 30 is calculated based on the electric energy consumption of theheater 32.

[Specific Processing of Embodiment 2]

Hereinafter, specific processing performed by the PM amount sensingdevice for exhaust gas according to Embodiment 2 will be described byusing FIG. 6. FIG. 6 is a flowchart of a routine performed by ECU 50 inEmbodiment 2. In Embodiment 2, a map of the correlation lines betweenW_(H) and the amount of PM are prestored in the ECU 50. This map can bedefined such that the larger the electric energy consumption W_(H) is,the larger the amount of PM becomes, as with the map of Embodiment 1 inFIG. 5.

In the routine of FIG. 6, first, step S100 described in Embodiment 1 isexecuted.

Next, the storing of I_(L1), I_(L2), and Gexh, and the calculation ofΔI_(L) are performed (step S208). In Embodiment 2, successive storageprocessing to repeatedly store (sample) the outputs I_(L1) and I_(L2) ofthe A/F sensors 22 and 24, respectively at a predetermined period (forexample, for every 8 milliseconds) is provided in the ECU 50. Moreover,in Embodiment 2, successive storage processing to store the exhaust gasamount Gexh at the same timing with the storing of the outputs I_(L1)and I_(L2) is also provided in the ECU 50. In step S208, the ΔI_(L)calculation processing of steps S108 and S110 is repeatedly performedbased on the storage values I_(L1), I_(L2), and Gexh of the abovedescribed successive storage processing. In Embodiment 2, the ECU 50continually executes these processing after step S208, and ΔI_(L) issuccessively updated to the latest value.

Next, step S104 described in Embodiment 1 is executed and the heater isturned off. Thereafter, as particulates go on accumulating in the filter30, the value of ΔI_(L) that is successively calculated graduallyincreases.

Next, when ΔI_(L) reaches a predetermined value, time count is started(step S213). This step allows that the time count is started at a stagewhere a predetermined level of particulates have accumulated in thefilter 30. This makes it possible to carry out the processing thereafterunder the situation where particulates are being surely trapped in thefilter 30. Consequently, it is realized that estimation accuracy of thecalculation of PM amount is ensured, and the electric energy consumptionof the heater under the condition where particulates are not beingtrapped is reduced.

Next, when the time that is started to count in step S213 reaches apredetermined time period (hereinafter, referred to as “T₁”), the heateris turned ON (step S214). After the heater 32 is turned ON, electricpower is supplied to the heater 32 at a predetermined amplitude P₀ and apredetermined duty ratio D_(H). At this time, the heater 32 iscontrolled so as to be able to heat the filter 30 at lease to atemperature not lower than the temperature at which particulates startto burn. Moreover, in Embodiment 2, time is counted after the heater 32is turned ON.

After the start of the control of the heater 32 in step S214, the filter30 is heated by the heater 32 and particulates in the filter 30 go onburning to be removed. As a result of this, the value of ΔI_(L)gradually decreases.

Thereafter, the electric energy consumption until ΔI_(L) becomes zero iscalculated (step S216). In Embodiment 2, first, the heater 32 is turnedON, and thereafter determination processing on whether or not ΔI_(L)becomes zero is performed. The counting of time is stopped at the timingwhen ΔI_(L)=0 is fulfilled, and a time period T_(H) from the ON time ofthe heater 32 to a time when ΔI_(L) becomes zero is obtained. Next,calculation processing to calculate the electric energy consumptionW_(H) based on the time period T_(H), the above described P_(o), and theduty ratio D_(H) (to be specific, for example, multiplication ofT_(H)×P_(o)×D_(H)=W_(H)) is executed. The calculated electric energyconsumption W_(H) is assumed to be the electric energy consumed by theheater 32 to remove particulates in the filter 30.

Next, the amount of PM according to the amount of exhaust gas iscalculated (step S218). In this step, first, the map of the correlationlines of W_(H) and the amount of PM stored in the ECU 50 is referred sothat the amount of PM according to W_(H) is calculated. Thereafter, aswith Embodiment 1, the amount of particulates per unit time and per unitgas amount are calculated based on the integrated exhaust gas amountGexh_itg and the predetermined time period T_(o).

Thereafter, the heater 32 is heated again so that particulates in thefilter 30 are removed (step S220). Thereafter, the process returns tostep S208, and the processing after step S208 are repeatedly executed.

According to the above described processing, it is possible to sense theamount of particulates in the exhaust gas.

It is noted that in Embodiment 2 described above, the filter 30corresponds to the “filter” in the tenth invention; and the heater 32 tothe “heater” in the tenth invention, respectively. Moreover, inEmbodiment 2, the “temperature reduction control” in the tenth inventionis implemented by the ECU 50 executing the processing of step S212; the“heating control means” in the tenth invention by the ECU 50 executingthe processing of step S213 and step S214; the “electric energy sensingmeans” of the tenth invention by the ECU 50 executing the processing ofstep S216; and the “calculation means” of the tenth invention by the ECU50 executing the processing of step S220, respectively in the routine ofFIG. 6.

Moreover, in Embodiment 2, the “determination means” in the eleventhinvention is implemented by the ECU 50 executing the determinationprocessing on whether or not ΔI_(L) is zero; and the “electric energycalculation means” in the eleventh invention by the ECU 50 executing thecalculation processing to calculate electric energy consumption W_(H)based on the time period T_(H), the above described P_(o), and the dutyratio D_(H), in step S216 of FIG. 6.

Moreover, although the hardware configuration is not illustrated inEmbodiment 2, the A/F sensor 22 corresponds to the “upstream side oxygenconcentration sensor” in the above described twelfth invention; and theA/F sensor 24 not shown corresponds to the “downstream side oxygenconcentration sensor” in the twelfth invention.

[Variant of Embodiment 2]

In the specific processing of Embodiment 2, the outputs of the A/Fsensors 22 and 24 when the predetermined time period T₁ elapsed arestored in step S214. The present invention, however, is not limited tothis configuration. The ECU 50 may store, in place of the time periodT₁, the outputs of the A/F sensors 22 and 24 when the integrated exhaustgas amount Gexh_igt reaches a predetermined amount.

The control of the heater 32 is not limited to the duty control as instep S214. For example, electric power may be supplied to the heater 32such that the resistance value (temperature of the heater 32) indicatesa predetermined value. In this case, the electric energy consumption maybe calculated such as by monitoring electric power consumption of theheater 32.

In Embodiment 2, variants include one as shown below. In this variant,when the predetermined time period has elapsed (or the exhaust gasintegrated value has reached a predetermined amount) after theheater-off processing in step S212, the processing after the heater-onprocessing in step S214 is executed. That is, in the present variant,the comparison of ΔI_(L) with a predetermined value in step S213 iseliminated.

Moreover, variants described in Embodiment 1 may be combined withEmbodiment 2.

Embodiment 3 Configuration of Embodiment 3

FIG. 7 is a diagram to show the configuration of an abnormalitydetection apparatus of an internal combustion engine relating toEmbodiment 3 of the present invention. The abnormality detectionapparatus of Embodiment 3 can detect abnormality of a diesel particulatefilter (DPF) 130 provided in the exhaust pipe 10. This abnormalitydetection apparatus can be used for OBD (On-board Diagnosis) while beingmounted on a vehicle.

In Embodiment 3, it is supposed that the internal combustion engine 2 isa diesel engine, and a heating mechanism (not shown) for regeneratingthe DPF 130 is provided. The ECU 50 can control the heating mechanism toregenerate the DPF 130.

There are already various known configurations regarding the heatingmechanism for the regeneration of DPF. Therefore, although detaileddescription will not be made, the DPF 130 may be heated by, for example,so-called post injection. To be specific, an exhaust fuel-addition valvemay be provided in the exhaust path of the internal combustion engine 2.The exhaust fuel-addition valve is provided to add fuel to the exhaustgas flowing in the exhaust path. By performing fuel addition with theexhaust fuel-addition valve at an appropriate timing, it is possible toregenerate the DPF 130. Moreover, so-called post injection may beperformed to perform fuel addition. Moreover, a heater may be attachedto the DPF 130 to heat the DPF 130 by this heater.

As shown in FIG. 7, A/F sensors 22 and 24 are provided in the upstreamand the downstream of the DPF 130 as with the filter 30 of Embodiment 1.In the DPF 130 as well, as in the filter 30, as the amount ofparticulates increases, ΔI_(L) increases. If the DPF 130 is in acondition to be able to normally trap particulates, the particulateswill go on to accumulate in the DPF 130, and the effect of theaccumulation of particulates should manifest itself in ΔI_(L).Therefore, it is possible to detect abnormality of the DPF 130 based onΔI_(L).

[Specific Processing of Embodiment 3]

FIG. 8 is a flowchart of the routine to be executed by the ECU 50 inEmbodiment 3. It is supposed that the routine of FIG. 8 is executedduring the startup of the internal combustion engine 2. In the followingdescription, description will be omitted or simplified as appropriate onoverlapping points in the contents with those of Embodiments 1 and 2.

In the routine of FIG. 8, first, heating to activate the A/F sensor isperformed as with step S100 of Embodiment 1 (step S300).

Then, DPF regeneration control is performed (step S302). In this step,the ECU 50 controls the heating mechanism, which has been alreadydescribed, so that particulates in the DPF 130 are removed.

Next, steps S102, S106, S108, and S110 are executed as in Embodiment 1.Thereby, the determination processing of A/F sensor activation, thedetermination processing of PM burning in DPF 130, the zero-pointcorrection processing of the output of the A/F sensor, the calculationprocessing of the integrated exhaust gas amount Gexh_itg, and thecalculation processing of ΔI_(L) are successively executed.

Next, the amount of PM is calculated (step S304). In this step, based onΔI_(L), the amount of PM is calculated according to correlation lines aswith the processing of step S112 of Embodiment 1. In Embodiment 3 aswell, a map of correlation lines as shown in FIG. 5 is created andstored in the ECU 50.

Next, it is determined whether or not the amount of PM is not more thana predetermined value (step S306). As described so far, if the DPF 130is in a condition to be able to normally trap particulates, particulatesshould go on accumulating in the DPF 130. When, contrary to such anexpectation, the amount of PM in the DPF 130 indicates a value not morethan the predetermined value, it is considered that an abnormality ofsome kind has occurred in the DPF 130. Therefore, the determination onwhether or not the amount of PM is not more than the predetermined valueis performed in Embodiment 3. When this condition is negated, it isjudged that the DPF 130 is normally trapping particulates, and theroutine of this round ends.

When the condition of step S306 holds, it is determined that there is anabnormality in DPF 130 (step S308). When the abnormality detectionapparatus of Embodiment 3 is being used for OBD, alerting the driver by,for example, lighting an alarm lamp is performed.

According to the above described processing, it is possible to performthe detection of abnormality in a particulate filter.

It is noted that, in Embodiment 3, after the amount of PM is calculatedfrom ΔI_(L), determination based on the comparison between the amount ofPM and the predetermined value is performed. The present invention,however, is not limited to this arrangement. The comparisondetermination may be made by comparing ΔI_(L) with a predetermined valuewithout performing the conversion to the amount of PM.

It is noted that in Embodiment 3 described above, the DPF 130corresponds to the “particulate filter” in the thirteenth invention, andthe A/F sensor 24 to the “oxygen concentration sensor” in the thirteenthinvention, respectively. Moreover, the “heating means” in the thirteenthinvention is implemented by the ECU 50 executing the processing of stepS302 in the routine of FIG. 8, and the “detection means” in thethirteenth invention by the ECU 50 executing the processing of stepsS110, S304, S306, and S308 in the routine of FIG. 8, respectively.

Moreover, in Embodiment 3 described above, the A/F sensor 22 correspondsto the “oxygen concentration sensor” in the fourteenth invention.

1. A PM sensor, comprising: an inlet port through which a portion of gasthat is drawn from an exhaust path of an internal combustion engine isallowed to flow in; a filter for filtering particulate matter (PM) inthe gas that has flowed in through the inlet port; a heater attached tothe filter and capable of changing the temperature of the filter; anoutlet port through which the gas that has passed through the filter isallowed to flow out to the exhaust path; and an oxygen concentrationsensor element disposed in the outlet port side and including a heater,wherein the oxygen concentration sensor is heated to a predeterminedtemperature by the heater upon being activated and is adapted to changeits output according to an oxygen concentration of gas that has passedthrough the filter, and wherein the oxygen concentration sensor isdisposed being spaced apart from the filter such that the filter has alevel of temperature at which particulate matter in the filter is notremoved when temperature of the oxygen concentration sensor itself is atthe predetermined temperature.
 2. The PM sensor according to claim 1,further comprising an oxygen concentration sensor element disposedbetween the inlet port and the filter and adapted to change its outputaccording to an oxygen concentration of gas that has flowed in throughthe inlet port.
 3. The PM sensor according to claim 2, wherein theoxygen concentration sensor element of the outlet port side and theoxygen concentration sensor element of the inlet port side are air-fuelratio sensor elements.
 4. (canceled)
 5. A PM amount sensing device forexhaust gas, comprising: a filter provided in an exhaust path of aninternal combustion engine and for filtering particulate matter (PM) inexhaust gas that flows through the exhaust path; an oxygen concentrationsensor element disposed in a downstream of the filter in the exhaustpath, and adapted to change its output according to an oxygenconcentration of gas that has passed through the filter; a heaterattached to the filter; heating control means for controlling the heatersuch that the filter is heated until particulate matter in the filter isremoved; temperature reduction control means for controlling the heatersuch that a temperature of the filter is not higher than a temperatureat which particulate matter in the filter is not removed, after thecontrol of the heating control means; acquisition means for acquiring anoutput of the oxygen concentration sensor element when a predeterminedtime period has elapsed after a temperature of the filter becomes nothigher than the temperature; means for calculating an integrated valueof an amount of exhaust gas that flows into the filter before anacquisition timing of the output by the acquisition means; andcalculation means for calculating an amount of particulate matter in theexhaust gas per unit time and per unit volume based on the outputacquired by the acquisition means, the predetermined time period, theand the integrated value.
 6. (canceled)
 7. The PM amount sensing devicefor exhaust gas according to claim 5, further comprising an oxygenconcentration sensor element disposed in an upstream of the filter inthe exhaust path, and capable of changing its output according to anoxygen concentration of exhaust gas that flows into the filter, whereinthe calculation means calculates an amount of particulate matter in theexhaust gas based on a difference between an output of the oxygenconcentration sensor element of the upstream side of the filter and anoutput of the oxygen concentration sensor element of the downstream sideof the filter.
 8. The PM amount sensing device for exhaust gas accordingto claim 7, wherein the oxygen concentration sensor element of thedownstream side of the filter and the oxygen concentration sensorelement of the upstream side of the filter are air-fuel ratio sensorelements.
 9. The PM amount sensing device for exhaust gas according toclaim 8, further comprising calibration means for calibrating an outputdeviation between the air-fuel ratio sensor of the downstream side ofthe filter and the air-fuel ratio sensor of the upstream side of thefilter.
 10. A PM amount sensing device for exhaust gas, comprising: afilter provided in an exhaust path of an internal combustion engine andfor filtering particulate matter (PM) in exhaust gas that flows throughthe exhaust path; a heater attached to the filter; an upstream sideoxygen concentration sensor disposed in an upstream of the filter in theexhaust path, and adapted to change its output according to an oxygenconcentration of gas that flows into the filter; a downstream sideoxygen concentration sensor disposed in a downstream of the filter inthe exhaust path, and adapted to change its output according to anoxygen concentration of gas that flows out from the filter; temperaturereduction control means for controlling the heater such that atemperature of the filter is not higher than a temperature at whichparticulate matter in the filter is not removed; heating control meansfor controlling the heater such that a temperature of the filter becomesnot lower than a temperature at which particulate matter in the filteris removed, after a predetermined period has elapsed since a temperatureof the filter becomes not higher than the temperature through thecontrol by the temperature reduction control means; electric energysensing means including: determination means for determining whether ornot particulate matter in the filter is removed based on a differencebetween an output of the upstream side oxygen concentration sensor andan output of the downstream side oxygen concentration sensor after astart of the control by the heating control means, electric energycalculation means for calculating electric energy consumption of theheater during a period from a start of the control by the heatingcontrol means until it is determined that particulate matter in thefilter is removed; and means for calculating electric energy consumptionconsumed by the heater for removing particulate matter in the filterbased on the electric energy consumption calculated by the electricenergy calculation means; and calculation means for calculating anamount of particulate matter of the exhaust gas based on the electricenergy consumption sensed by the electric energy sensing means. 11-15.(canceled)
 16. A PM amount sensing device for exhaust gas, comprising: afilter provided in an exhaust path of an internal combustion engine andfor filtering particulate matter (PM) in exhaust gas that flows throughthe exhaust path; an oxygen concentration sensor element disposed in adownstream of the filter in the exhaust path, and adapted to change itsoutput according to an oxygen concentration of gas that has passedthrough the filter; a heater attached to the filter; a heating controlunit for controlling the heater such that the filter is heated untilparticulate matter in the filter is removed; a temperature reductioncontrol unit for controlling the heater such that a temperature of thefilter is not higher than a temperature at which particulate matter inthe filter is not removed, after the control of the heating controlunit; an acquisition unit for acquiring an output of the oxygenconcentration sensor element when a predetermined time period haselapsed after a temperature of the filter becomes not higher than thetemperature; an unit for calculating an integrated value of an amount ofexhaust gas that flows into the filter before an acquisition timing ofthe output by the acquisition unit; and a calculation unit forcalculating an amount of particulate matter in the exhaust gas per unittime and per unit volume based on the output acquired by the acquisitionunit, the predetermined time period, the and the integrated value.
 17. APM amount sensing device for exhaust gas, comprising: a filter providedin an exhaust path of an internal combustion engine and for filteringparticulate matter (PM) in exhaust gas that flows through the exhaustpath; a heater attached to the filter; an upstream side oxygenconcentration sensor disposed in an upstream of the filter in theexhaust path, and adapted to change its output according to an oxygenconcentration of gas that flows into the filter; a downstream sideoxygen concentration sensor disposed in a downstream of the filter inthe exhaust path, and adapted to change its output according to anoxygen concentration of gas that flows out from the filter; atemperature reduction control unit for controlling the heater such thata temperature of the filter is not higher than a temperature at whichparticulate matter in the filter is not removed; a heating control unitfor controlling the heater such that a temperature of the filter becomesnot lower than a temperature at which particulate matter in the filteris removed, after a predetermined period has elapsed since a temperatureof the filter becomes not higher than the temperature through thecontrol by the temperature reduction control unit; an electric energysensing unit including: a determination unit for determining whether ornot particulate matter in the filter is removed based on a differencebetween an output of the upstream side oxygen concentration sensor andan output of the downstream side oxygen concentration sensor after astart of the control by the heating control unit, an electric energycalculation unit for calculating electric energy consumption of theheater during a period from a start of the control by the heatingcontrol unit until it is determined that particulate matter in thefilter is removed; and an unit for calculating electric energyconsumption consumed by the heater for removing particulate matter inthe filter based on the electric energy consumption calculated by theelectric energy calculation unit; and a calculation unit for calculatingan amount of particulate matter of the exhaust gas based on the electricenergy consumption sensed by the electric energy sensing unit.